The present invention relates to clutches, and more particularly, relates to an active bidirectional overrunning clutch.
The use of clutches in an all wheel drive vehicle system has been known for years. In a typical all wheel drive system, the front axle is a primary drive, while torque to the rear axle is only transferred when the front wheels spin faster than the rear wheels. The torque transfer generally occurs if the front wheels have excessive slip and it also can occur during low speed cornering situations and the like. The use of a clutch in an all wheel drive vehicle system works as a mechanical disconnect which prevents torque from being transferred from the rear axle to the front axle. Prior art clutches currently include single direction clutches, bidirectional overrunning clutches, and even clutches that use hydraulic systems to effect changes thereon. The bidirectional overrunning clutch differs from the single directional, in that it works in both the clock wise and counter clock wise rotational directions. During operation of the bidirectional clutch, if the output of the rear axle is rotating faster in one direction than the input from the front axle due to a gear ratio offset, there is no torque transmission, but if the input speed is equal to the output speed the unit will lock. Furthermore, if the bidirectional clutch is used in an all wheel drive system and is in four wheel drive while in the reverse gear, the overrunning clutch locking function direction must be changed from the forward direction to the reverse direction. The bidirectional clutch will switch the operation mode dependent upon the prop shaft or input speed direction. The use of the bidirectional overrunning clutch provides benefits with regards to braking, stability, handling, and drive line durability.
In the typical ABS braking event disconnecting the front and rear drive lines during braking assists in maintaining braking stability. During ABS braking events the locking of the rear wheels is avoided for stability reasons and hence the brake systems are designed to lock the front wheels first. Thus, any torque transfer during an ABS event from the rear axle to the front axle may disturb the braking system because of the potential for instabilities on the slippery road surfaces. The use of the bidirectional overrunning clutch decouples the rear drive once the rear wheels spin faster than the front wheels and provides excellent braking stability.
A bidirectional clutch also reduces the likelihood of throttle off over steering during cornering of the vehicle. During a throttle off maneuver the clutch decouples the rear drive line thus forcing all of the engine braking torque to the front wheels which reduces the possibility of a lateral slip on the rear axle. This condition forces the vehicle to under steer on a throttle off condition, a situation which is considered easier to manage by the average vehicle operator.
The use of bidirectional clutches with an all wheel drive system provides several advantages. However, difficulties sometimes occur during low speed operation when a vehicle is in a reverse rolling position and the vehicle operator selects a drive position. Once the operator accelerates a back lash occurs in the drive line which allows inertia in the engine and other components to build thus transmitting a torque to the rear drive line which may induce an NVH (noise vibration harshness) phenomenon within the bidirectional mechanism as the vehicle drive line moves from the reverse gear to a forward gear. This NVH phenomenon is undesirable in current new vehicle markets. Therefore, there is a need in the art for a bidirectional clutch mechanism that has active indexing which will reduce the NVH phenomenon associated with a switch from a forward to reverse gear and a reverse to forward gear in an all wheel drive vehicle system.
One object of the present invention is to provide an active bidirectional overrunning clutch capable of being indexed.
Another object of the present invention is to provide an active pin and slot indexing system for use with a bidirectional overrunning clutch.
Yet a further object of the present invention is to provide a clutch with an active indexing that will reduce the NVH phenomenon associated with prior art bidirectional clutch mechanisms.
Still another object of the present invention is to provide a clutch that will index during rotation reversal before torque is transmitted through a prop shaft of the vehicle.
Yet a further object of the present invention is to provide a bidirectional clutch that can be set in a neutral position and will completely disconnect the clutch and allow the rear axle to spin freely, thus operating similar to a part time on demand system.
To achieve the forgoing objects the active bidirectional clutch includes an oil housing. The clutch also includes a flange which is rotatably supported with respect to the oil housing. The clutch also includes an input shaft which is rotatably fixed with respect to the flange. A coupling is located adjacent to the input shaft. The clutch includes a plurality of rollers in contact with the input shaft and the coupling. A roller cage will position the plurality of rollers with respect to the input shaft and the coupling. The clutch also includes a sleeve which is positioned around the input shaft, wherein the sleeve has a plurality of slots. The sleeve is also connected to the roller cage.
One advantage of the present invention is that active indexing of the bidirectional clutch will occur prior to torque transfer.
A further advantage of the present invention is a reduction of the NVH phenomenon by actively indexing the bidirectional clutch mechanism.
A still further advantage of the present invention is the reduction in speed difference between the prop shaft and the rear axle pinion shaft because of the indexing of the clutch, which therefore locks the clutch before any torque transmission.
Yet another advantage of the present invention is the use of a neutral position which will disconnect the clutch from the drive train and let the rear axle spin freely thus acting like a part-time on demand system.
Still another advantage of the present invention is the low speed indexing of the clutch from either the reverse to the forward gear or vice versa.